Thermite method of abandoning a well

ABSTRACT

A well abandonment tool comprises a housing locatable within a wellbore, the housing including a compartment containing sealing material, an activator to initiate the release of the sealing material, an anchor for securing the tool in the wellbore, and a slickline for deploying the housing in the wellbore. The sealing material may be thermite, and the activator may be an ignitor that initiates the thermite reaction. The ignitor may include a battery and element, the activation process includes making a contact such that the battery causes the element to heat to ignite the thermite.

Over the past 20 years or so a large number of offshore structures have been constructed which are now or will soon be exhausted and will need to be abandoned. These offshore structures may comprise production platforms which are either steel or concrete structures resting on the sea bed or floating platforms. Numerous conduits are connected to these offshore structures to carry the various fluids being gas, oil or water etc., which are necessary for the production of oil and/or gas from the well.

In abandoning a well, consideration has to be given to the potential environmental threat from the abandoned well for many years in the future.

In the case of offshore structure there is usually no rig derrick in place which can be used to perform the required well abandonment procedure. Therefore it is typically necessary to install a new derrick or alternatively a mobile derrick can be positioned above the well. This requirement adds considerable expense to the task of abandoning the offshore well, compared to a land based well.

A typical production well will comprise a number of tubular conduits arranged concentrically with respect to each. The method of abandoning the well which is presently known in the art involves the separate sealing of each of the concentric conduits which requires a large number of sequential steps.

In the abandonment method known in the art the first step is to seal the first central conduit usually by means of cement or other suitable sealant. The first annular channel between the first and second conduits is then sealed and the first central conduit is then cut above the seal and the cut section is removed from the well.

The second annular channel between the second and third conduits is then sealed and the second conduit cut above the seal and the cut section is removed from the well.

This process is repeated until all the conduits are removed. The number of separate steps required is typically very large indeed and the number of separate operations is five times the number of conduits to be removed. This adds considerably to the cost of the well abandonment due to the time taken and the resources required at the well head.

It is the purpose of the present invention to provide a method of abandoning a well which avoids the disadvantageous and numerous operations which are required by the existing known methods. This will greatly reduce the costs of safely abandoning a well. It is a further objective of the invention to provide a method of abandoning a well without the requirement of a rig which involves significant expense particularly in subsea based wells.

It is a further advantage of the invention to isolate an inner tubing string of a wellbore. Furthermore the method of abandonment of the well will comply with all the regulatory guidelines for the isolation of a well.

According to the present invention there is provided a well abandonment tool according to claim 1 and a method of abandoning a well according to claim 13.

According to the present invention there is provided a method of abandoning a well, by assembling a modular tool assembly which consists of an ignitor, thermite and anchor and deploy into a well on slickline.

According to another aspect of the present invention the entire operation will be performed with mechanical operations, such as pressuring the tubing above the tool to set the slips and the actuation of the ignitor by the release of the running tool.

According to another aspect of the invention, the slickline will have a fibre optic cable in its ID, the fibre optic cable will provided distributed sensing of the thermite reaction and also set the anchor slips and initiate the thermite ignitor.

Using fibre optic cable is advantageous over initiating firing using a conductive cable, as stray electromagnetic fields that may be found at a well rig may induce a current in conductive cabling and prematurely trigger firing initiation. The fibre-optic cable can also be utilised to gather sensor feedback.

According to a further aspect of the invention, when the tool reaches a pre-defined temperature a low temperature alloy part melts and the slickline is separated cleanly from the tool assembly deployed.

According to a further aspect of the invention, additional modules of materials can be deployed to either consume more casing, or seal any cracks or fissures generated by the heat of the thermite reaction using low temperature alloy. Essentially, further devices may be lowered on top of each other and activated, either simultaneously or sequentially.

According to a further aspect of the invention the sealing material deployed could be a two part resin deployed mixed using a static mixing discharge head.

According to a further aspect of the invention, the ignition process can only commence when the running tool is disconnected from the assembly

According to a further aspect of the invention, the ignition process could be the mixing of two reactive chemicals

According to a further aspect of the invention, the ignition process could be the closing of an electrical contact to enable a battery to heat an element which in turn ignites the thermite

According to further aspect of the invention, the fibre optic cable has superior safety for initiating the activation of the thermite ignitor than electrical methods using electrical signals from surface

According to a further aspect of the invention the fibre optic cable provides feedback of the thermite process in real time and other sensor methods.

According to a further aspect of the invention, a very high current (>10 amps) is required to activate the initiator, so no stray currents could accidentally initiate the ignitor.

Thus by means of the method according to the invention the number of operations required is greatly reduced, thus resulting in a considerable reduction in the cost of carrying out the well abandonment.

The following is a more detailed description of an embodiment according to invention by reference to the following drawings in which:

FIG. 1 A,B,C,D Is a section side view through different tool modules which are connected together and deployed as an assembly on slickline incorporating fibre optics.

FIG. 2 A,B is a section side view of the lower most part of the assembly which is detail A from FIG. 1D, in its two states of operation.

FIG. 3 A,B Is a similar component to FIG. 2 , with the same two states of operation, with the addition of a pressure seal cup.

FIG. 4 is detail B from FIG. 1D and shows in detail the mechanical and optical termination of each module.

FIG. 5 is detail C from FIG. 1C and shows in detail an internal optical splitter and how it is aligned with a low energy ignitor.

FIG. 6 is detail D from FIG. 1A and shows in detail the slickline termination and two modes of operation incorporating a low temperature alloy means of providing an automatic release mechanism once the thermite reaction has commenced.

FIG. 7 is a similar view to FIG. 6 , and shows in detail the slickline termination and two modes of operation incorporating a shear pin release mechanism, so that in the event the assembly gets stuck the slickline can be recovered, by overpulling and shearing the pins.

FIG. 8 A, B, C,D is a section side view through surface pressure control hardware and illustrates the deployment sequence of two modules.

FIG. 9 A,B is a section side view through different tool modules which are connected together and deployed as an assembly on regular slickline

FIG. 10 A,B is a section side view of the lower most part of the assembly which is detail E from FIG. 9B, in its two states of operation.

FIG. 11 A,B is detail E from FIG. 9A and shows in detail the uppermost part of the tool assembly, and how the mechanical initiated ignitor is initiated after jarring to release the GS running tool (not shown); and

FIG. 12 A,B is a similarly arrangement to FIG. 11 A, B and shows the uppermost part of the tool assembly, and on releasing the GS running tool (not shown) a mechanical rod is pulled upwards, which closes an electrical contact and initiates the thermite ignitor.

FIG. 13 is a section side view through a first slickline deployed tool

FIG. 14 is a section side view through a second and a required number of more slickline deployed tool

FIG. 15 is a section side view through a third from last

FIG. 16 is a section side view through a second from last

FIG. 17 is a section side view through the last tool to be deployed

FIG. 18 is a section side view through the tools shown in FIGS. 13 to 17 assembled

Referring to FIGS. 1 to 7 , there is shown a means of mechanical and optically terminating a small diameter metal clad fibre optic tube. The metal clad tube 5 is made up of several layers (previously disclosed in for example in patent no US2004118590), so that to grip onto all of the layers and ensure all the layers carry the load, small balls 4 are used which provide low stress points of grip, these are energised by ramps 7 when the nut 8 is made tight. The balls are retained in a body 9, which when screwed into housing 10 also energises a metal to metal seal 11 which seals the metal to metal tube 5 to the housing 10. The housing 10 is shear pin attached 12 to a no rotating connector body termination 13. In the event the tool string gets stuck, the slickline 5 can be overpulled and the shear pins 14 will fail and the fibre optic slickline together with the remaining part of the connector 15 can be recovered to surface. The fibre 3 inside the metal clad tube is fed into a precision fibre optic termination 16 which is retained in the bore 17 of the housing 10. The excess fibre is cut and the face polished 18 to ensure minimum losses. An optical 19 and mechanical 20 connection coupling consists of a male 21 and female 22 half is fitted to the end of each tool. This enables the tool modules 23 to be connected without turning the fibre optic connection. The optical connection is protected by a sleeve 24 and a seal 25. At the upper end of each tool module is a reduced external diameter section 26 which provides a positive location to hold the assembly during installation into the well.

At the lower most end of the assembled tool is a means of anchoring the tool to the inside of the tubing it is lowered inside. It consists of a taper 30, and a collet 31 (commonly called slip) which is prevented from moving up the taper surface by a pin 32 which passes through a rod 33, which is prevented from moving up by a solid block of chemically reactive material 34 consisting of a blend of aluminium powder, metal oxides, carbon, sulphur, potassium perchlorate, potassium chloride and sucrose. The optical connector is embedded 35 into the solid chemical block, when a laser beam is supplied down the fibre, when about 6-7 joules of energy has been applied, this chemical block ignites and reduces very quickly to a fraction of its original volume, this allows the rod 33 to move up into the now void space 36 by the force of the spring 37. This also pushes the slips 31 up onto the taper 30 pushing them into the outward direction so they can grip into the tubing (not shown) and anchor the tool.

The lowest part of the assembly could also include a seal 40 which provides a mechanical pressure barrier. While lowering the assembly into the well, ideally this seal should not be active, so the fluid below the tool can bypass the seal through the central passage 41 around a non-return valve 42 and through radial holes 43, 44. When the slips have been activated, the rod 45 moves up to its set position 46. In this position, the radial hole 43 is now across a blank pipe 47 and flow is no longer possible

Further up the tool assembly is a module which contains thermite 50 and a thermite ignitor 51. This again uses energy transmitted via the fibre optic cable, a single fibre 52 passes through the tool, and fibre optic splitter is used to provide two fibre 54, 55 where required, so the fibre 54 continues through to the lower optical termination and the fibre 55 is terminated into a connector which penetrates into another chemically reactive block 51. This block requires more energy to react typically 15-16 joules, so it cannot be set of when setting the lowermost anchor.

The fibre inside the tool is also a distributed sensor, in its simplest sensing mode it will measure temperature, this is very helpful as it will confirm the different operations have worked as required, together with monitoring the hanging weight of the slickline, the slickline operator can lower the assembly if he sees weight dropping off, as this will indicate the thermite is being consumed. Inside tubing this will not be significant, but if the slickline tube is inside the casing outside the tubing, then it will drop significantly as the volume of the casing is much larger.

The temperature can be monitored up to the destruction of the tool and fibre.

As the temperature around and up the tool increases, an automatic release mechanism allows the slickline to make a clean and controlled separation from the thermite reaction happening below the slickline connector. This automatic release, consists of a release joint 70, 71 being held together by a block of low temperature alloy 72 or bismuth. When assembled, the bismuth is melted and poured into the void 72 and sets. The bismuth is held in compression by the taper surfaces 73, 74. When the bismuth melts there is a large clearance between the diameters 75,76 and the tapers 73,74 prevent hang up. An optical connector 77, 78 allows a clean optical break, so the slickline is free to come back to surface.

Referring to FIG. 8 A,B,C,D there is shown a means of deploying multiple tool modules, these could have different functions such as Low temperature or retarded thermite, high temperature thermite, low temperature alloy or bismuth, thermal barrier, anchor or bridge plug.

Typically, tool stings are limited by the length of the lubricator 80, this is a pressure vessel extension that goes on top of the well, together with blow out preventer 81. In our case a longer tool string than conventional lubricators can allow is desirable. The following describes the deployment sequence, which can be repeated to achieve the required length and composition of tool string.

The first tool module is picked up inside the lubricator, the lubricator is connected to a quick connector 82, inside the connector is fitted a split landing ring 83. The tool is lowered into the well until an oversized collar 84 lands on the ring 83. This precisely locates the deployment bar 85 in line with insertable clamps 86, these support the weight of the tool assembly in the well and provide a pressure seal around the deployment bar.

The connector can then be disconnected and the next module 87 picked up and connected to the module 88 in the well, the split clamp can then be refitted, the lubricator reconnected and the next module lowered into the well. This can be repeated as required.

Referring to FIG. 9 to 11 , there is shown another embodiment of the invention. In this embodiment, the slickline used to deploy the assembly has no intelligence, so all the operations are mechanical in nature to achieve the same outcome.

In this example there is shown a toolstring consisting of only two modules, this could be more as earlier described. The lower tool module 90 consists of a thermal barrier 91, anchor 92 pressure seal 93 and upper male termination 94. The second module 95 consists of a lower female connector 96, which makes up to the male termination 94. The upper end of the tool consists of an internal GS profile 97 into which a standard GS running tool can engage (this is well understood by anyone knowledgeable in the slickline industry).

To activate the slips of the anchor 92, once at the required setting depth, pressure is applied at surface, this is seem across the piston area 98 which shears the pins 99 and allows the slips 100 to set and engage the tubing not shown. This could also be achieved by a rapid deceleration of the tool string, the momentum in the downward direction of the mandrel 130 would be sufficient to apply enough force to shear the shear pins 99.

Once set, the jars can be activated on the GS running tool to disconnect the running tool from the GS profile 101. The running tool is slightly modified from normal, in that it has a collet which engages the profile 102. As the GS tool is pulled free, it pulls up the rod 103 to its uppermost position until the collet unlatches from the profile 102.

As soon as the rod 103 moves in the upward direction it causes the failure of fragmentable plate 104. This plate together with seal 105,106,107 hermetically seals the chamber 108.

The chamber 108 is filled with glycerine, and material below the plate 104 is KMnO4 109. When these two mix they generate a very hot mixture which is sufficient to ignite the thermite 110 below it.

Referring to FIGS. 12 A and B the rod 103 is used in a similar way to that shown above, in that when the GS running tool is disconnected, the rod is pulled upward to its uppermost position, The lower end of the rod 103 is connected to a ignitor module 114, this has an electrical heating element inside it and a small quantity of easy to ignite chemical mixture. Two electrical connectors protrude from its upper surface. When the rod 103 is pulled up to its uppermost position, the electrical connectors 115, 116, are docked into mating connectors 117, 118, these in turn are connected to three lithium 4.4 volt 30 amp batteries 121 connected in series, once the circuit is complete the batteries cause the heating element to glow red hot, which in turn ignites the small amount of chemical mixture which turns molten hot 119, this drops onto the thermite 120.

Referring to FIGS. 13 to 18 there is shown another embodiment of a slickline tool. It would be installed into the well in several runs, that is, the tool is formed of modules which can be run into the well separately with each module being connected to the module previously run into the well, so any desired length of thermite can be deployed. Typically, in well operations, tool strings of about 30 ft are only possible, in this example we have 5 separate runs into the well, so this assembly could be in the order of (5×30 ft) 150 ft.

The first module consists of a pressure set anchor, surface pressure (or some pre-determined pressure) is applied and the check valve 240 moves a sleeve 241 downwards, this activates two slips 242, 243, this lock the anchor to the tubing, and the seal 244 provides a mechanical barrier for the bismuth to fall under gravity on top of. Above the seal in the tool string is a thermal barrier 245 this is a ceramic or silica flour or sand material to protect the anchor from the heat generated by the thermite 246 above. At the very top of the tool is a standard GS running profile 247, in which a standard slickline tool can engage and disengage.

The next tool has a collet 248 to dock into the profile 247. This tool just contains thermite 249, and any number of these can be run depending how long a thermite plug is desired.

Referring to FIG. 15 , another embodiment of the tool is similar to the previous tool, but with the addition of a mechanically operated ignitor. It has a slightly modified upper profile 250, which works in combination with the lower profile of the next tool 251. When profiles 250 and 251 are connected, the collet 252 locates into the profile 253, a second collet 254 connects to the profile 255, now these rods are permanently connected, finally, a tool with tungsten carbide balls is connected to provide a seal and weight.

To activate the ignitors, the tool string is extended, the collet 252 can travel longitudinally in the recess 253, the rods 254, 255 move which breaks the seals 260, 261, on one side of the seal is glycerine 262, 263, and on the other is potassium permanganate 264, 265 and magnesium ribbon 266, 267. Thus we have two ignitors for the thermite.

At the top of the chamber 270, inside the housing is high temperature thermite 202, the base has a deflector 271 which directs the ignited thermite out of ports 272, the ports 272 are filled with a low temperature material such as bismuth or plastic to keep the thermite isolated from the wellbore fluids. When the thermite exits the port it hits the ID tubing 205 and cuts through it. Above the thermite is a housing containing bismuth, this both provide both a weight and later forms a seal after it has flown down the annular path around the tool and ID of the tubing, and forms a permanent metal to metal seal above the mechanical seal 244.

An alternative arrangement could be a plug which has a ceramic or tungsten carbide deflector, and ceramic or tungsten carbide piston rings, these contain the thermite reaction and direct the energy to sever the tubing, in addition the plug could have a set of one way slips which prevent the plug being displaced up the tubing, but allow the free movement down of the plug. Above the plug could be additional weight provided by cartridges of ceramic or tungsten carbide balls 

1. A well abandonment tool comprising: a housing locatable within a wellbore, the housing including a compartment containing sealing material an activator to initiate the release of the sealing material an anchor for securing the tool in the wellbore a slickline for deploying the housing in the wellbore.
 2. A well abandonment tool according to claim 1 wherein the sealing material is thermite, and the activator is an ignitor that initiates the thermite reaction
 3. A well abandonment tool according to claim 1 wherein the ignitor includes a battery and element, the activation process includes making a contact such that the battery causes the element to heat to ignite the thermite.
 4. A well abandonment tool according to claim 1 wherein the sealing material is two part resin deployed, and the activator includes a static mixing discharge head.
 5. A well abandonment tool according to claim 1 wherein the sealing material is two co-reactive chemicals.
 6. A well abandonment tool according to claim 1 wherein the sealing material is a low temperature alloy such as bismuth
 7. A well abandonment tool according to claim 1 wherein the anchor is set by pressuring the wellbore above the tool
 8. A well abandonment tool according to claim 1 wherein the tool is deployed on a running tool, the running tool being releasably secured to the tool by a low melting point material, such that the melting of the low melting point material releases the running tool.
 9. A well abandonment tool according to claim 1 wherein the tool is deployed on a releasable running tool, and the ignitor is actuated by release of the running tool.
 10. A well abandonment tool according to claim 1 wherein the slickline includes a fibre optic cable in its inner diameter.
 11. A well abandonment tool according to claim 1 wherein the fibre optic cable transmits sensed data from the well abandonment tool.
 12. A well abandonment tool according to claim 1 wherein the sensed data includes the temperature or activation of the sealing material.
 13. A well abandonment tool according to claim 1 wherein the fibre optic cable interfaces with the thermite such that the thermite reaction can be initiated using the fibre optic cable.
 14. A method of abandoning a well tool comprising the steps of: deploying a first tool according to claim 1; and releasing the first tool from the slickline and activating the thermite deploying a second tool according to claim 1 releasing the second tool from the slickline and activating the thermite. 